Heart failure affects approximately three million Americans, developing in about 400,000 each year. It is currently one of the leading admission diagnoses in the U.S. Recent advances in the management of acute cardiac diseases, including acute myocardial infarction, are resulting in an expanding patient population that will eventually develop chronic heart failure.
Current therapy for heart failure is primarily directed to using angiotensin-converting enzyme (ACE) inhibitors and diuretics. While prolonging survival in the setting of heart failure, ACE inhibitors appear to slow the progression towards end-stage heart failure, and substantial numbers of patients on ACE inhibitors have functional class III heart failure. Moreover, ACE inhibitors consistently appear unable to relieve symptoms in more than 60% of heart failure patients and reduce mortality of heart failure only by approximately 15-20%. Heart transplantation is limited by the availability of donor hearts. Further, with the exception of digoxin, the chronic administration of positive inotropic agents has not resulted in a useful drug without accompanying adverse side effects, such as increased arrhythmogenesis, sudden death, or other deleterious side effects related to survival. These deficiencies in current therapy suggest the need for additional therapeutic approaches.
A wide body of data suggests that pathological hypertrophy of cardiac muscle in the setting of heart failure can be deleterious, characterized by dilation of the ventricular chamber, an increase in wall tension/stress, an increase in the length vs. width of cardiac muscle cells, and an accompanying decrease in cardiac performance and function. Studies have shown that the activation of physiological or compensatory hypertrophy can be beneficial in the setting of heart failure. In fact, the effects of ACE inhibitors have been purported not only to unload the heart, but also to inhibit the pathological hypertrophic response that has been presumed to be linked to the localized renin-angiotensin system within the myocardium.
On a molecular biology level, the heart functions as a syncytium of myocytes and surrounding support cells, called non-myocytes. While non-myocytes are primarily fibroblast/mesenchymal cells, they also include endothelial and smooth muscle cells. Indeed, although myocytes make up most of the adult myocardial mass, they represent only about 30% of the total cell numbers present in heart. Because of their close relationship with cardiac myocytes in vivo, non-myocytes are capable of influencing myocyte growth and/or development. This interaction may be mediated directly through cell--cell contact or indirectly via production of a paracrine factor. Such association in vivo is important since both non-myocyte numbers and the extracellular matrix with which they interact are increased in myocardial hypertrophy and in response to injury and infarction. These changes are associated with abnormal myocardial function.
Cardiac myocytes are unable to divide shortly after birth. Further growth occurs through hypertrophy of the individual cells. Cell culture models of myocyte hypertrophy have been developed to understand better the mechanisms for cardiac myocyte hypertrophy. Simpson et al., Circ. Res., 51: 787-801 (1982); Chien et al., FASEB J., 5: 3037-3046 (1991). Most studies of heart myocytes in culture are designed to minimize contamination by non-myocytes. See, for example, Simpson and Savion, Cir. Cres., 50: 101-116 (1982); Libby, J. Mol. Cell. Cardiol., 16: 803-811 (1984); Iwaki et al., J. Biol. Chem., 265: 13809-13817 (1990).
Shubaita et al., J. Biol. Chem., 265: 20555-20562 (1990) documented the utility of a culture model to identify peptide-derived growth factors such as endothelin-1 that can activate a hypertrophic response. Long et al., Cell Regulation, 2: 1081-1095 (1991) investigated the effect of the cardiac non-myocytes on cardiac myocyte growth in culture. Myocyte hypertrophic growth was stimulated in high-density cultures with increased numbers of non-myocytes and in co-cultures with increased numbers of non-myocytes. This effect of non-myocytes on myocyte size could be reproduced by serum-free medium conditioned by non-myocyte cultures. The major myocyte growth-promoting activity in the cultures was heparin binding. The properties of this growth factor were compared to various growth factors known to be present in myocardium, including fibroblast growth factor (FGF), platelet derived growth factor (PDGF), tumor necrosis factor-alpha (TNF-.alpha.), and transforming growth factor-beta1 (TGF-.beta.1). The growth factor of Long et al. was found to be larger than these other known growth factors and to have a different heparin-Sepharose elution profile from that of all these growth factors except PDGF. Further, it was not neutralized by a PDGF-specific antibody. The authors proposed that it defines a paracrine relationship important for cardiac muscle cell growth and development.
Not only is there a need for an improvement in the therapy of heart failure such as congestive heart failure, but there is also a need to offer effective treatment for neurological disorders. Neurotrophic factors such as insulin-like growth factors, nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, -4, and -5, and ciliary neurotrophic factor have been proposed as potential means for enhancing neuronal survival, for example, as a treatment for neurodegenerative diseases such as amyotrophic lateral sclerosis, Alzheimer's disease, stroke, epilepsy, Huntington's disease, Parkinson's disease, and peripheral neuropathy. It would be desirable to provide an additional therapy for this purpose.
Accordingly, it is an object of the present invention to provide an improved therapy for the prevention and/or treatment of heart failure such as congestive heart failure, particularly the promotion of physiological forms of hypertrophy or inhibition of pathological forms of hypertrophy, and for the prevention and/or treatment of neurological disorders such as peripheral neuropathy.
It is another object to identify a novel group of cardiac hypertrophy factor polypeptides and antagonists thereto for use in such therapies.
It is yet another object to provide nucleic acid encoding such polypeptides and to use this nucleic acid to produce the polypeptides in recombinant cell culture.
It is a still further object to provide derivatives and modified forms of such polypeptides, including amino acid sequence variants and covalent derivatives thereof.
It is an additional object to prepare immunogens for raising antibodies against such polypeptides, as well as to obtain antibodies capable of binding them.
It is still another object to provide a novel hypertrophy assay that can be used, for example, in expression cloning and purification of such polypeptides, in evaluation of clones isolated from the expression cloning, and in identification of antagonists to such polypeptides.
These and other objects of the invention will be apparent to the ordinarily skilled artisan upon consideration of the specification as a whole.